Field of the Invention
The invention relates to a high-power pulse-transformer for short high-voltage and/or high-current pulses, preferably for high-power laser circuits, including at least one magnet core having self-enclosed magnet legs disposed around a central window and having two wide sides of the magnet core with axes being normal to the axis of the window, at least one undervoltage winding and at least one overvoltage winding wrapped around the magnet core and linked to the magnet core and to each other, the windings having turns of electrically insulated metallic conductors being substantially doubly-wound relative to each other.
Such a high-power pulse transformer is known from publication (1) listed below. However, before discussing such a device in detail, the fundamental nature of the device will be discussed.
Direct coupling, high-power, pulse engineering often does not succeed in matching the load resistance to the characteristic resistance of a pulse generating network. Furthermore, the switching elements which are capable of switching voltages and currents according to a given application, are often lacking.
The use of high-power pulse transformers, which may also be referred to simply as pulse transformers, offers a possibility of circumventing such technical difficulties. The possible functions of such devices are, inter alia: current matching, voltage matching, impedance matching, potential separation, and potential reversal.
Several applications of such devices will be discussed in detail below. When charging a pulse-generating network with dielectric liquid, as is described in European patent application No. 0 024 576, which is publication (2) listed below, especially in FIG. 11 thereof, it would be technically advantageous for the charge to come from a thyristor-switched power supply. Thyristors can switch relatively high currents at low holding voltages. The pulse-generating network is to be charged to voltages of several tens of kV in the .mu.sec range
In order to match the low voltage in the thyristor circuit to the high-voltage in the pulse-generating network, a resonance transformer, such as is described in publication (3) listed below, may be used. However, in this specific case the charging time of the pulse-generating network is several milliseconds. In order to achieve charging within a few .mu.sec, it is necessary to employ a pulse transformer with a leakage inductance that is reduced to a minimum.
Due to the high leakage inductances which are inherent in the structure of conventional high-voltage transformers, they cannot transform the specified energies in that short period of time. Another requirement is the ability to operate the transformer at high repetition rates, which are also referred to by the abbreviation PRR (Pulse Repetition Rate). The problem of effectively dissipating heat developing in devices which must be compact, is then encountered.
Regarding the problems involved in the field of application of high-power transformers of the above-described type, reference must also be made to supplying an X-ray flash tube in order to generate high-intensity X-ray pulses in the submicrosecond range, especially at high repetition rates. In the trigger circuit for the X-ray flash tube, both the pulse-generating network and the switching element may be structured for the required X-ray tube acceleration voltage, as seen in publications (4), (5) and (6) listed below. The disadvantage of these conventional devices lies in the required high dielectric strength of the components and the accompanying technological difficulties, especially at high repetition rates.
Another possibility for triggering an X-ray tube is to tap the supply pulse for the X-ray tube at the secondary side of a pulse transformer. Descriptions of such devices can be found in publications (4) and (7). In such a method, difficulties are encountered when energies that are as high as possible are to be transformed in the shortest possible time In order to increase the cut-off frequency of a transformer for such high voltages and simultaneous low impedance, a very close coupling for reducing the internal voltage drop and the least possible leakage inductance, are desirable. This necessitates minimization of the insulating spacings between secondary and primary windings and between the core and the windings, which leads to extremely high electrical field strengths because of the high voltages.
While the high-power pulse transformer according to publication (1) listed below which is the starting point for the invention of the instant application, already has the desired short pulse length it must be noted that the transformation ratio drops considerably at relatively high load resistances, relative to the no-load transformation ratio. Other technical disadvantages of this conventional pulse transformer become apparent, especially at high voltages and during continuous operation. Given the electrical field strength which must be very high and the short rising time pulses, corona effects appear even in carefully selected and processed dielectrics, resulting in irreparable destruction of the dielectric and accordingly the failure of the transformer. Additionally, at high repetition rates and high mean outputs, a solid dielectric would render the dissipation of unavoidably developing heat from the soft magnetic core, extremely difficult.
The general problem underlying the invention deals with overcoming the difficulties occurring in high-power pulse transformers according to publication (1) listed below, which further reduces the leakage inductance of the prior art, which avoids the corona effects or increases the dielectric strength and which improves the heat dissipation.
This general problem also applies to another conventional pulse transformer according to publication (8) listed below, which is formed of an assembly of stacked, lamellar windings with dielectric layers therebetween. In this case as well, the problem of dielectric strength is also present because electrical field strength at the edges of the lamellar conductors automatically lead to early destruction during extended operation, due to corona effects. Additionally, the boundary surfaces between the solid dielectric and the conductors are considerably stressed mechanically by current forces, which also lead to electrical punctures. Therefore, the leakage inductance which must be relatively low, cannot be utilized and the electrical insulation is too prone to trouble.
It is accordingly an object of the invention to provide a high-power pulse transformer for short high-voltage and/or high-current pulses, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type for short high-voltage and/or high-current pulses which, beyond the general objects:
is usable for current matching, voltage matching, impedance matching, potential separation and potential reversal, in other words especially for a so-called "step-up" transformer which generates pulses of higher voltages at optimal power transformation, but is also a so-called "step-down" transformer which generates short pulses of very high amperage, while high-voltage pulses are transformed down and fed into a very low-resistance load. While the iron losses outweigh the copper losses in the step-up transformers, the losses in the conductors must be kept low in the step-down (current) transformers, by optimizing the winding cross sections;
is suitable for supplying an X-ray flash tube for generating X-ray pulses in the submicrosecond range with high intensity and especially at high repetition rates; and
has a sufficiently high cut-off frequency at simultaneously low internal resistance, when operated as a step-up transformer, in particular for triggering an X-ray flash tube, while the undervoltage and overvoltage windings are very closely coupled, with the least possible leakage inductance at the same time.